Heart disease, specifically coronary artery disease, is a major cause of death, disability, and healthcare expense in the United States and other industrialized countries. A number of methods and devices for treating coronary artery disease have been developed, some of which are specifically designed to treat the complications resulting from atherosclerosis and other forms of coronary arterial narrowing.
One method for treating such vascular conditions is percutaneous transluminal coronary angioplasty (PTCA). During PTCA, a balloon catheter device is inflated to dilate a stenotic blood vessel. The stenosis may be the result of a lesion such as a plaque or thrombus. When inflated, the pressurized balloon exerts a compressive force on the lesion, thereby increasing the inner diameter of the affected vessel. The increased interior vessel diameter facilitates improved blood flow.
However, soon after the procedure, a significant proportion of treated vessels restenose. Various methods have been developed to prevent or inhibit this restenosis. One method is to provide a physical support in the form of a stent to maintain the increased interior diameter of the vessel lumen.
Stents are generally cylindrical shaped devices that are radially expandable to hold open a segment of a vessel or other anatomical lumen after implantation into the body lumen. Various types of stents are in use, including expandable and self-expanding stents. Expandable stents generally are conveyed to the area to be treated on balloon catheters or other expandable devices. For insertion, the stent is positioned in a compressed configuration along the delivery device. The stent may be crimped onto a balloon that is folded or otherwise wrapped about a guide wire that is part of the delivery device. After the stent is positioned across the lesion, it is expanded by the delivery device. For a self-expanding stents, a sheath is retracted that allows expansion of the stent.
Stents have been used with coatings to deliver drugs or other therapeutic agents at the site of the stent to assist in preventing inflammation, infection, thrombosis, and proliferation of cell growth that can occlude the vessel lumen. However, the coated stent can deliver drugs to only those portions of the vessel in contact with the stent. Because restenosis is often a greater problem in tissue adjacent to the ends of a stent than it is elsewhere along the stent, drug delivery using the stent alone may not be fully effective.
One drawback of current drug eluting stent technology is that the drug is combined with a polymer. In such drug coated stents the drug and polymer need to be combined in a common solution or suspension, thereby making it necessary to use a common solvent. In addition, when the drug is fully eluted the stent is left with non-functional polymer on the stent surface, which may be less biocompatible than the stent material itself.
Vascular delivery of drugs and other agents intended to inhibit restenosis has also been accomplished using devices that inject or otherwise infuse the agents into the treated portion of the vessel before, during, or after performing PTCA. Unlike coated stents, these devices deliver the anti-restenosis agents without providing physical support for the treated vessel. One drawback to these devices is that the drug is delivered in discrete targeted locations within the tissue wall which may limit the effectiveness of the drug for limiting restenosis.
Thus, coated stents support the lumen of a vessel in an open position following PTCA but may be limited in their ability to deliver an anti-restenosis agent to the wall of the treated vessel. Therefore, it would be desirable to have a system and method for treating a vascular condition that overcome the aforementioned and other disadvantages.